2015 Thompson Educational Publishing, Inc. 3. What Are Nutrients?

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1 2015 Thompson Educational Publishing, Inc. 3 What Are Nutrients? Nutrients are chemical substances obtained from food and used by the body for many different processes. They are the raw materials our bodies need to supply energy, to regulate cellular activities, and to build and repair tissues. All organisms including humans require nutrients to perform their life functions and to obtain the energy necessary for survival.

2 The Three Energy Nutrients t Carbohydrates istockphoto.com/ Roman Chmiel t Proteins t Fats istockphoto.com/ og- vision/olgalis istockphoto.com/ Ka<v

3 The Three Key Energy Nutrients The food we take in contains three key energy nutrients that are broken down over the course of digestion: Carbohydrates Protein Fats Of these three key nutrients, carbohydrates are our most important source of energy Thompson Educational Publishing, Inc. 3

4 The Central Role of Carbohydrates in Supplying Energy Carbohydrates are the most abundant organic substances in nature, and they are essential for human and animal life. Sugars and starches are examples of carbohydrates. The main functions of carbohydrates are to provide materials to build cell membranes and to provide energy for use by cells. Glucose is the usual form in which carbohydrates are assimilated by humans. Glucose is stored within skeletal muscle and within the liver as glycogen Thompson Educational Publishing, Inc. 4

5 Approximate Energy Sources for Different Types of Sport Activities 2015 Thompson Educational Publishing, Inc. 5

6 ATP The Common Energy Molecule To be usable, nutrients in the food we eat need to be reconstituted (or resynthesized) into a universal form of energy a free energy that can then be used for muscle contraction and many other physiological processes. Adenosine Triphosphate (ATP) The final form this free energy takes is adenosine triphosphate, ATP the common energy molecule for all living things. ATP captures the chemical energy resulting from the breakdown of food and is then used to fuel the various cellular processes in our bodies Thompson Educational Publishing, Inc. 6

7 The Release of Energy from ATP Energy is released when a trailing phosphate atom is broken from the ATP molecule. This results in ADP (adenosine diphosphate plus energy), as in the formula below: ATP > ADP + P + Energy 2015 Thompson Educational Publishing, Inc. 7

8 The Problem of Resynthesizing ATP In high demand by the body, ATP energy supplies are used up very quickly. The problem becomes how to resynthesize new supplies of ATP to ensure that bodily functions continue. There are two methods for resynthesizing ATP: anaerobic (without oxygen) and aerobic (with oxygen) Thompson Educational Publishing, Inc. 8

9 Two Energy Systems The anaerobic system occurs without the requirement of oxygen. It can occur in two separate metabolic pathways, one not involving the breakdown of glucose and the other involving the partial breakdown of glucose. The aerobic system, a separate but to some extent overlapping energy system, requires oxygen. It involves many enzymes and several complex sub-pathways, and it leads to the complete breakdown of glucose. (Fats and protein also enter the cycle at this stage.) 2015 Thompson Educational Publishing, Inc. 10

10 Three Metabolic Pathways There are two energy systems (anaerobic and aerobic), but there are three metabolic pathways by which ATP energy reserves are restored. They are: ATP-PC (anaerobic alactic) Glycolysis (anaerobic lactic) Cellular respiration In the presence of oxygen, the second pathway (glycolysis) is also the beginning of the third pathway (the aerobic system) Thompson Educational Publishing, Inc. 10

11 Three Metabolic Pathways ATP-PC System (anaerobic alactic) Glycolysis (anaerobic lactic) Cellular respiration (aerobic)

12 ATP-PC (Anaerobic Alactic) This pathway draws on processes deep within the muscle fibre itself. It allows for quick, intense muscle contraction. It is alactic lactic acid is not a byproduct Thompson Educational Publishing, Inc. 12

13 Glycolysis (Anaerobic Lactic) This pathway involves the partial breakdown of glucose, with lactic acid a byproduct. It does not involve oxygen and is therefore anaerobic. It allows for longer bursts of energy Thompson Educational Publishing, Inc. 13

14 Cellular Respiration The aerobic system (cellular respiration) is the main source of energy during endurance events. It involves oxygen and the complete breakdown of glucose. It yields large amounts of ATP Thompson Educational Publishing, Inc. 14

15 The ATP-PC Pathway The ATP-PC pathway relies on the action of phosphocreatine, a compound normally stored in muscle and readily accessible, to sustain the levels of ATP required during the initial phase of short but intense activity. This is the first and the simplest of the two anaerobic energy pathways Thompson Educational Publishing, Inc. 15

16 Amount of ATP This Pathway Yields The ATP-PC pathway yields enough ATP (one molecule) for about seconds of strenuous effort. Intense activities that are of short duration (for example, the shotput, weightlifting, the 100-metre sprint) rely heavily on the ATP-PC pathway. This system is referred to as anaerobic alactic because the ATP-PC system does not yield lactic acid as a byproduct Thompson Educational Publishing, Inc. 20

17 The Chemical Equation for the ATP-PC Pathway Phosphocreatine (PC) is a high-energy molecule in which the phosphate can be broken off easily and which can be used to convert ADP (adenosine diphosphate) back to ATP. The chemical equation that represents this process is as follows: 2015 Thompson Educational Publishing, Inc. 17

18 The ATP-PC (Anaerobic Alactic) Pathway 2015 Thompson Educational Publishing, Inc. 18

19 The ATP-PC Energy Pathway in Sports In sports, the ATP-PC system plays an important role in such power events as the 50- and 100-metre dash, the high jump, and Olympic weightlifting. Such events last only a few seconds and require a large burst of energy. ATP-PC is important in these events because it provides the highest rate of ATP resynthesis that cannot be matched by other, more complex energy systems Thompson Educational Publishing, Inc. 19

20 Activities Relying on the ATP-PC Pathway 2015 Thompson Educational Publishing, Inc. 20

21 Glycolysis (Anaerobic Lactic) Glycolysis is the body s second (anaerobic) energy pathway. The ATP produced in this pathway allows a person to engage in a high level of performance for about an additional 90 seconds. The pathway is described as anaerobic lactic because lactic acid is a byproduct of this process. In the absence of oxygen, the buildup of lactic acid is painful and further activity is hampered Thompson Educational Publishing, Inc. 21

22 Amount of ATP Glycolysis Yields Like ATP-PC, this second metabolic pathway is also capable of producing ATP fairly rapidly and without the need for oxygen. Glycolysis is considerably more complex than the ATP-PC pathway. In fact, glycolysis involves eleven separate biochemical reactions. Glycolysis yields twice as much ATP as the ATP-PC pathway (i.e., two molecules of ATP for every molecule of glucose) Thompson Educational Publishing, Inc. 22

23 The Chemical Equation for Glycolysis Through a series of chemical reactions, glycolysis transfers energy from glucose and rejoins phosphate to ADP (adenosine diphosphate). The chemical equation that represents glycolysis is as follows: 2015 Thompson Educational Publishing, Inc. 23

24 The Glycolysis (Anerobic Lactic) Pathway 2015 Thompson Educational Publishing, Inc. 24

25 Glycolysis in Sports Sports that rely heavily on the anaerobic lactic energy pathway (glycolysis) involve short bouts of effort for longer periods of time. Examples are sports such as medium-distance track and speedskating events, and alternating shifts in ice hockey. Such sports are eventually hampered by the buildup of lactic acid. In the absence of adequate oxygen supplies, pyruvic acid the main product of glycolysis is converted to lactic acid and exhaustion or painful muscle agony begins to set in quickly. The short shifts in a game of hockey perhaps capture this process best Thompson Educational Publishing, Inc. 25

26 Activities Relying on Glycolysis 2015 Thompson Educational Publishing, Inc. 30

27 Cellular Respiration Cellular respiration refers to the process in which the body s cells use oxygen to generate energy through the various metabolic pathways found in the mitochondria of cells Thompson Educational Publishing, Inc. 27

28 Amount of ATP This Pathway Yields The ATP produced by cellular respiration far exceeds the ATP produced by the other two pathways. Ultimately, 36 molecules of ATP are produced (or a couple more, depending on the fuel source) for every molecule of glucose nearly 20 times the number of ATP molecules produced by the anaerobic energy system. This aerobic metabolic pathway leads to the complete breakdown of glucose Thompson Educational Publishing, Inc. 28

29 Chemical Equation for Cellular Respiration In the presence of oxygen, cellular respiration can, in theory, sustain activity for a very long time, or until other physiological limits are reached. This is the pathway that underlies endurance-type events (eg., a marathon run). The chemical equation that represents this process is as follows: 2015 Thompson Educational Publishing, Inc. 29

30 The Three Sub-Pathways (Stages) Comprising Cellular Respiration Cellular respiration actually involves three separate sub-pathways: Glycolysis Krebs cycle (also known as the citric acid cycle ) Electron transport chain 2015 Thompson Educational Publishing, Inc. 30

31 The Cellular Respiration (Aerobic) Pathway 2015 Thompson Educational Publishing, Inc. 31

32 Cellular Respiration, Sports, and Energy Sources For any athlete to sustain intense activity longer than 90 seconds or so, cellular respiration must come into prominence. Endurance sports such as soccer that involve continuous effort over a lengthy time period rely heavily on cellular respiration. Fats and proteins in addition to glucose are used as energy sources during this phase. During physical exercise, the primary sources of energy are carbohydrates and fats; protein is less accessible and normally contributes only a small percentage of the total energy used Thompson Educational Publishing, Inc. 32

33 Activities Relying on Cellular Respiration 2015 Thompson Educational Publishing, Inc. 33

34 Factors Affecting ATP Energy Production for Life Processes The preceding description of the three pathways is a simplifed representation of the chemistry involved. In real life and everyday activity, the processes and pathways overlap and interact in complex ways. The three metabolic pathways allow our bodies to create sufficient energy to carry out movement as well as all vital processes neural activity, organ function, breathing, and so on. The precise ways in which these pathways are used for ATP energy production also depends on the individual athlete, the sport the athlete is involved in, and the intensity and duration of physical activity Thompson Educational Publishing, Inc. 34

35 A Comparison of the Three Metabolic Pathways in the Human Body 2015 Thompson Educational Publishing, Inc. 35

36 Slow-Twitch and Fast-Twitch Muscle Fibres Certain muscles and muscle groups are more adapted to one energy production system than another. Exercise physiologist find it useful to distinguish different kinds of muscle fibres: Slow-twitch muscle fibres are red or dark in colour, and generate and relax tension relatively slowly. The trade-off is that they are able to maintain a lower level of tension for long durations. Fast-twitch muscle fibres are more pale in colour, have the ability to tense and relax quickly, and can generate large amounts of tension with relatively low endurance levels Thompson Educational Publishing, Inc. 36

37 Muscle Fibre Types and Physical Activity Slow-twitch muscle fibres These are ideal for activities such as longdistance swimming, cycling, and running. Fast-twitch muscle fibres These can activate at a rate two to three times faster than slow-twitch muscles, making them ideal for the fast, powerful muscle contractions needed for activities such as short sprints, powerlifting, and explosive jumping Thompson Educational Publishing, Inc. 37

38 Type I Fibres [Slow-Oxidative (SO) Muscle Fibres] Kinesiologists distinguish not just two but three different types of muscle fibre, using a combination of tension-generating features and the metabolic properties of the fibre. Type I or slow-oxidative (SO) muscle fibres generate energy slowly, are more fatigueresistant, and primarily depend on aerobic processes Thompson Educational Publishing, Inc. 38

39 Three Fibre Types t Type I or Slow-Oxidative (SO) v Generate energy slowly v Fatigue-resistant v Depend on aerobic processes t Type IIA or Fast-Oxidative Glycolytic (FOG) v Intermediate-type muscle fibres v Allow for high-speed energy release v Allow for glycolytic capacity t Type IIB of Fast-Glycolytic (FG) v Store glycogen and high levels of enzymes v Allow for quick contraction without the need for oxygen

40 Type IIA Fibres [Fast-Oxidative Glycolytic (FOG) Fibres] Type IIA or fast-oxidative glycolytic (FOG) muscle fibres are intermediate-type muscle fibres. They allow for high-speed energy release as well as glycolytic capacity Thompson Educational Publishing, Inc. 40

41 Type IIB Fibres [Fast-Glycolytic (FG) Muscle Fibres] Type IIB or fast-glycolytic (FG) muscle fibres store lots of oxygen and sufficiently high levels of enzymes necessary for quick contraction without requiring oxygen Thompson Educational Publishing, Inc. 41

42 Characteristics of Muscle Fibre Types 2015 Thompson Educational Publishing, Inc. 42

43 The Role of Myoglobin in Sustaining Energy-Producing Reactions The differences in muscle fibre types are due mainly to the extent to which a muscle relies on oxygen in the production of energy. The protein myoglobin is the oxygen storage unit that delivers oxygen to working muscles, thereby enabling energy-producing reactions to be sustained over a long time period. Slow-twitch, red muscle fibres are high in myoglobin and ideal for endurance activities. Fast-twitch fibres (with low myoglobin concentrations) are more adapted to shorter bursts of effort Thompson Educational Publishing, Inc. 43

44 Approximate Distribution of Muscle Fibre Types for Different Sports

45 Implications for Training For elite athletes, differences in muscle fibre types are often very pronounced. Olympic sprinters, for example, may possess as much as percent fast-twitch muscle fibres. Athletes in marathon-style events may possess that equivalent in slow-twitch fibres. But many factors contribute to an individual s athletic performance. Physiology is just one of them Thompson Educational Publishing, Inc. 45

46 The Puzzle of East Africans Dominance in Distance Running For some time now, athletes from Kenya and Ethiopia have dominated longdistance running. These countries typically account for medals in the 5000 m, the m, and the 42.2 km marathon. The achievement of these runners is one of the most puzzling and most studied topics in sport science Thompson Educational Publishing, Inc. 46

47 Consistently Outstanding Results for East African Men and Women On the men s side, the world records in competitions ranging from the 800 m to the marathon show that 17 of 21 records are held by East Africans. On the women s side, Ethiopian Triunesh Dibaba won gold at the 2012 Olympics in the m, and two Kenyan women won silver and bronze. In the 5000 m event in London, Dibaba s teammate Mesaret Defar won gold, with Vivian Cheruiyot placing second and Dibaba placing third. (Dibaba had also won the m race at the 2008 Olympic Games in Beijing Thompson Educational Publishing, Inc. 60

48 Victory for Kenya & Ethiopia at the World Athletics Championships, Thompson Educational Publishing, Inc. 48

49 Possible Physiological and Cultural Explanations Some researchers theorize that these athletes bodies have a higher capacity to take in and use oxygen a capacity known as VO2 max. Others argue that low overall body fat, long legs, and low resting heart rates help these athletes run faster, longer, and more efficiently. Children in Kenya and Ethiopia tend to walk and run everywhere, thus building up a strong background in long-distance running. Budding athletes in these countries often see running as a means of supporting their families through prize money and endorsements Thompson Educational Publishing, Inc. 49